用硬件加速内容截图WKWebview

Question

当有硬件加速的内容(一些特定的赌场游戏运行在iframe内)时，我在拍摄WKWebview内容的屏幕截图时遇到了严重的问题。到目前为止，我按照每个人的建议，使用了截图的标准方式：

UIGraphicsBeginImageContextWithOptions(containerView.frame.size, true, 0.0)

containerView.layer.render(in: UIGraphicsGetCurrentContext()!)

//This line helps to fix view rendering for taking screenshot on older iOS devices
containerView.drawHierarchy(in: containerView.bounds, afterScreenUpdates: true)

let image = UIGraphicsGetImageFromCurrentImageContext()!

UIGraphicsEndImageContext()

这个方法非常好地工作，直到我在我的WKWebview中得到一些由GPU呈现的内容。GPU呈现的内容在屏幕截图上显示为黑色。我尝试了使用这种方法可以使用的所有技巧，但是没有任何帮助。即使是XCode视图层次结构调试器也不能显示硬件加速的内容。因此，与安卓类似，需要另一种方式来截图。我已经解决了Android上的类似问题，开始记录屏幕上发生的一切，并在获得第一张图像后停止屏幕记录。

我已经经历了无数的堆栈溢出问题和解决方案，但它们都是在Obj(我完全不擅长的)，过时或只是不够具体的我的需要。

现在我发现，我可以使用glReadPixels直接读取OpenGL中的像素(如果我的内容被硬件加速了，那么我就可以从显卡读取这些像素了，对吧？)

到目前为止，我已经成功地创建了一个Swift片段，可以执行类似于renderBuffer -> frameBuffer -> glReadPixels ->映像的操作。

let width = Int(containerView.frame.size.width)
let height = Int(containerView.frame.size.height)

//BeginImageContext code was run above

let api = EAGLRenderingAPI.openGLES3
let context2 = EAGLContext(api: api)
EAGLContext.setCurrent(context2)

// Setup render buffer
var renderBuffer : GLuint = GLuint()

let size = GLsizei(10)
glGenRenderbuffers(size, &renderBuffer)
glBindRenderbuffer(GLenum(GL_RENDERBUFFER), renderBuffer)
let bufferWidth = GLsizei(width * 1)
let bufferHeight = GLsizei(height * 1)
let bufferFormat = GLenum(GL_RGBA8)
glRenderbufferStorage(GLenum(GL_RENDERBUFFER), bufferFormat, bufferWidth, bufferHeight)

// Setup frame buffer
var frameBuffer = GLuint()
glGenFramebuffers(GLsizei(10), &frameBuffer)
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), frameBuffer)
glFramebufferRenderbuffer(GLenum(GL_FRAMEBUFFER), GLenum(GL_COLOR_ATTACHMENT0), GLenum(GL_RENDERBUFFER), renderBuffer)

// Draw
glReadBuffer(GLenum(GL_RENDERBUFFER))
glClearColor(0.1, 0.2, 0.3, 0.2)
glClear(GLbitfield(GL_COLOR_BUFFER_BIT))

//--------------
let bytes = malloc(width*height*4)
let bytes2 = malloc(width*height*4)

let x : GLint = GLint(0)
let y : GLint = GLint(0)
let w : GLsizei = GLsizei(width)
let h : GLsizei = GLsizei(height)

glReadPixels(x, y, w, h, GLenum(GL_RGBA), GLenum(GL_UNSIGNED_BYTE), bytes)

let data = NSData(bytes: bytes, length: width * height * 4)
let dataProvider = CGDataProvider(data: data)
//let dataProvider2 = CGDataProvider(dataInfo: nil, data: bytes!, size: width * height * 4, releaseData: )
let colorspace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo: CGBitmapInfo = [.byteOrder32Little, CGBitmapInfo(rawValue: CGImageAlphaInfo.last.rawValue)]
let aCGImage = CGImage(
    width: Int(width),
    height: Int(height),
    bitsPerComponent: 8,
    bitsPerPixel: 32,
    bytesPerRow: 4 * Int(width),
    space: colorspace,
    bitmapInfo: bitmapInfo,
    provider: dataProvider!,
    decode: nil, 
    shouldInterpolate: true,
    intent: .defaultIntent
    )!
let imaag = UIImage(cgImage: aCGImage)
//I get the image of the same color that is defined at clearColor

现在我的问题是，我走的路对不对？我是否有可能以某种方式将我的WKWebview (或对其进行快照并将其制作为UIView)发送到renderBuffer / frameBuffer，以便glReadPixels能够真正读取屏幕上的？

PS！我已经看到了许多关于如何让UIImage退出CAEAGLView的问题，但在我的例子中，不是CAEGLView，而是WKWebview。非常感谢。

Answer 1

我有一个简单的方法来拍摄快照，这是代码。

- (void)screenLoogShoot:(void (^)(UIImage *fullImage))snapShotHandler {
    WKWebView *webView = self.webView;
    UIScrollView *scrollView = webView.scrollView;
    CGFloat boundsWidth = scrollView.bounds.size.width;
    CGFloat contentHeight = scrollView.contentSize.height;
    CGFloat scale = [UIScreen mainScreen].scale;
    CGRect oldFrame = self.webView.frame;

    if (@available(iOS 11.0, *)) {
        self.webView.frame = CGRectMake(0, 0, boundsWidth, contentHeight);
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            WKSnapshotConfiguration *configuration = [WKSnapshotConfiguration new];
            configuration.rect = CGRectMake(0, 0, boundsWidth, contentHeight);
            configuration.snapshotWidth = @(boundsWidth);
            [self.webView takeSnapshotWithConfiguration:configuration completionHandler:^(UIImage * _Nullable snapshotImage, NSError * _Nullable error) {
                UIGraphicsBeginImageContextWithOptions(CGSizeMake(boundsWidth, contentHeight), NO, scale);
                [snapshotImage drawInRect:CGRectMake(0, 0, boundsWidth, contentHeight)]; 
                UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();
                UIGraphicsEndImageContext();
                self.webView.frame = oldFrame;
                snapShotHandler(fullImage);
            }];
        });
    } else {
        self.webView.frame = CGRectMake(0, 0, boundsWidth, contentHeight);
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            UIGraphicsBeginImageContextWithOptions(CGSizeMake(webView.bounds.size.width, webView.bounds.size.height), NO, scale);
            [webView drawViewHierarchyInRect:CGRectMake(0, 0, boundsWidth, contentHeight) afterScreenUpdates:YES];
            UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
            self.webView.frame = oldFrame;
            !snapShotHandler ? : snapShotHandler(fullImage);
        });
    }
}